The present invention relates to scanning documents and particularly to scanning books.
Scanned images of book pages often have three types of distortions generated by scanning. Depending on the book's orientation relative to the scanning direction when it lays on the scanning surface and the elevation of the book spine area above the surface, these three types of distortion appear at different levels. As shown in FIG. 1, when the book spine is above the scanning surface the scanned image usually has shadows appearing in the image close to the spine (“shadow distortion”). “Squeeze distortion” happens when the page image squeezes toward the spine and consequently the text closer to the spine becomes thin and difficult to recognize. The other type of distortion, “curvature distortion,” happens for the same reason but only when a book is scanned with its spine parallel to the scanner sensor bar, referred to as the “parallel scanning case.” In this case, the text close to spine also bends toward the center of the page. The abovementioned distortions not only affect the image's visual readability but also cause failures in the processing of Optical Character Recognition in the affected area. The present invention provides a method to detect the presence of the distortions and to correct distortions.